1. Field of the Invention
The present invention relates to concrete construction and more particularly, the present invention is directed to a concrete slip dowel which allows for continuous pours.
2. Background Information
U.S. Pat. Nos. 2,152,751; 3,437,018; 4,578,916; 4,733,513; 4,959,940; 5,005,331; 5,216,862; 5,487,249; 5,678,952; 5,797,231; 5,934,821; 6,502,359 provide, collectively, a meaningful background discussion in this field noting that in the art of concrete construction, it is commonplace to form joints between two or more poured concrete slabs allowing for thermal expansion of each slab. This type of joint is called an expansion joint. An expansion joint is formed by the placement of compressible materials consisting typically of wood or, more commonly, a composite fiber material at regular intervals of the concrete structure between the slabs. The compressible material allows expansion of the concrete, after curing, beyond its original volume. In order to prevent preventing buckling or relative angular displacement between adjacent slaps at such joints, it is common practice to insert steel dowel rods, generally known as “slip dowels”, within the edge portions of adjoining concrete slabs in such a manner that the concrete slabs may slide freely, i.e. “slip”, along the axis of the slip dowel or dowels, thereby permitting linear expansion and contraction of the slabs while at the same time maintaining the slabs in a common plane and thus preventing undesirable bucking or unevenness of the slabs at the joint.
A second such joint that controls contraction due to loss of moisture during curing is a control joint. Control joints are more prevalent and must be placed every 100 to 200 square feet of surface area. While a control joint protects the concrete slab from damage due to contraction of the concrete during curing and expansion or contraction thereafter within the slab itself, the joints prohibit loads placed on the concrete slab to be transferred uniformly throughout. As a result, control joints, without further reinforcement, leave the concrete slabs susceptible to damage. For instance, loads developed by a forklift moving across a non-reinforced control joint poses a serious risk of damage to the slab because the forklift's load at the control joint is supported by only one half of the volume of concrete as available to support the forklift in an portion of the slab without a control joint.
This coupling of adjacent slabs with a slip dowel represents an accepted load transfer methodology between the slabs, as noted by the American Concrete Institute (ACI) in 224.3R-205.2.4 that states “Load transfer is accomplished through aggregate interlock, through preformed key, or by the use of a doweled joint.” ACI also noted that “For dowels to be effective, they should be smooth, aligned and supported so they will remain parallel in both the horizontal and the vertical planes during the placing and finishing operation. Properly aligned, smooth dowels allow the joint to open as concrete shrinks.” (See ACI 302.1R-10 3.2.7) Further ACI notes that “The dowels should be centered on the joint. To permit horizontal movement, dowels must not bond to the concrete on at least one side.” (See ACI 224.3R-20 5.2.4.). In addition to control or expansion joints, these joints are also referenced apparently collectively, as “cold joints” in the art as cited in U.S. Pat. Nos. 5,005,331 and 5,487,249.
As noted, in order to function effectively, slip dowels must be accurately positioned parallel within the adjoining concrete slabs. The non-parallel positioning of the dowels will prevent the desired slippage of the dowels and will defeat the purpose of the “slip dowel” application. Additionally, the individual dowels must be placed within one or both of the slabs in such a manner as to permit continual slippage or movement of the dowels within the cured concrete slab(s).
U.S. Pat. No. 4,449,844 discloses similar slip dowel construction for concrete but addressing specific issues associated with highway concrete construction. Similarly U.S. Pat. No. 4,648,739 is related to concrete road construction and associated slip dowel usage, with this patent stating that doweled transverse joints are designed to provide load transfer between adjacent concrete panels, confine pavement cracking to predetermined locations directly over the steel dowel bar assemblies and minimize faulting of concrete panels at the joint area, but that the type of transverse joints currently utilized (at the time of filing of the patent application issuing as the '739 patent) “has been recognized by Federal Research studies as the cause of 90 to 95 percent of all concrete pavement performance problems” and wherein this “deficiency limits the life of otherwise durable concrete material to 15 to 25 years of services”.
The prior art dowels are often made of rebar, however smooth, lubricated, or coated entirely with plastic structures are known as disclosed in U.S. Pat. No. 3,397,626. The designs are developed to prevent the dowel from bonding to the concrete and allow the concrete slab or structure to slide relative to the dowel in a direction substantially perpendicular to the axis defined by the joint. Such movement of the slab relative to the dowel prevents build up of stress in the dowel that may result in cracking of the concrete.
In the prior art, several general methods of installing “slip dowels” have become popular. The following descriptions of existing methods will reference analogous components by reference numeral from the drawings showing the applicant's invention in an effort to better illustrate the operation of the prior art and to better highlight the advantages of the present invention. The following description of the known systems is not intended to suggest that the invention set forth in the figures of this patent application is a prior art system or method. A detailed description and understanding of the prior art methods and slip dowel systems will make the description of the present invention simple and allow the advantages to be more fully understood
i. Drilling into an Edge of a First Pour
According to a first method, a first concrete pour (similar to slab 18 in the attached drawings) is made within a pre-existing form. After the first pour has cured, an edge of the form (usually a wooden stud, similar to frame member 14 in the attached drawings) is stripped away. A series of holes are then drilled parallel into the first pour or slab 18 along the exposed edge from which the form or member 14 has been removed. The depth and diameter of the individual holes varies depending on the application and the relative size of the concrete slabs 18 to be supported. As a general rule, however, such holes are at least twelve (12) inches deep and typically have a diameter of approximately five-eighths (⅝) of an inch.
After the parallel aligned series of holes has been drilled into the first pour or slab 18, dowel rods (generally formed of rebar) are advanced into each such hole such that one end of each dowel rod is positioned within the first pour and the remainder of each dowel rod extends into a neighboring area where a second slab (such as slab 20 of the attached figures) of concrete is to be poured. Thereafter, concrete is poured into such neighboring area and is permitted to set with the parallel aligned dowels extending into the area of the second slab 20 pour. After the second pour or slab 20 has set, the slip dowels will be held firmly within the second slab but will be permitted to slide longitudinally within the drilled holes of the first slab thereby accommodating longitudinal expansion and contraction of the two slabs while at the same time preventing buckling or angular movement there between.
Although the above described “drilling method” of placing slip dowels has become well known, it will be appreciated that such method is extremely labor intensive. In fact, it takes approximately ten minutes to drill a five-eighths inch diameter by twelve inches long hole into the first pour, and the drilling equipment, bits, accessories, and associated set up time tends to be very expensive. Moreover, the laborers who drill the holes and place the slip dowels must be adequately trained to insure that the dowels are arranged perpendicular to the joint but parallel to one another so as to permit the desired slippage during subsequent use. Further the drilling is often through the expansion joint members (such as expansion member 16) used between adjacent concrete slabs 18 and 20.
ii. Sleeved Slip Dowel Set Method
A second popular method of placing slip dowels involves the use of slip sleeves, such as wax treated cardboard sleeves or premade plastic sleeves, positioned over one end of each individual dowel. According to such method, a series of holes are drilled through one edge of a concrete form (such as frame member 14) and smooth dowels are advanced through each such hole. Slip sleeves (similar to sleeve 12 of FIGS. 1-5) are placed over one end of each dowel and the first pour is made within the form, with the form holding the sleeved slip dowels in place. After the first pour has set forming a slab 18, the previously drilled form is stripped away, thus leaving the individual dowels extending into a neighboring open space where the second pour for an adjacent slab 20 is to be made. Subsequently, the second pour is made and permitted to cure forming an adjacent slab 20. Thereafter, the slip dowels will be firmly held by the concrete of the second pour or slab 20 but will be permitted to longitudinally slide against the inner surfaces of the slip sleeves 12 within the first pour. Thus, the slip sleeves 12 facilitate longitudinal slippage of the dowels, while at the same time holding the two concrete slabs 18 and 20 in a common plane, and preventing undesirable buckling or angular movement thereof.
This second method, while presently popular, is nonetheless associated with numerous deficiencies and is also labor intensive.
iii. Slip Sleeve Set Method
Another method known in the art which has become very popular is the use of slip sleeves 12 that are removeably mounted to and supported on one edge of the concrete form or frame member 14 in generally parallel relation to each other via base portions (no analogous member in the drawings) secured to the form or frame member 14, with a first pour being made thereabout to form slab 18. After the first pour has cured to form slab 18, the edge of the concrete form to which the slip sleeves 12 are mounted is stripped away from the first slab 18 together with the allegedly reusable mounting bases (basically ½ a dowel rod) leaving only the slip sleeves 12 within the first slab 18. The slip dowels are then advanced into the exposed open ends of the slip sleeves 12 embedded within the first slab 18. Those portions of the dowel rods not advanced into the slip sleeves extend into a neighboring area where a second pour of concrete is to be made to form adjacent slab 20. The pouring of the concrete into the neighboring area encapsulates the dowel rods which are held firmly within the second slab 20 formed by the curing of the second pour. The dowels, though being firmly held within the second slab 20, are permitted to slide longitudinally within the sleeves 12 (also called tubes) embedded in the first slab 18.
This method is currently commercialized by under the SPEED DOWEL™ brand by the Greenstreak company.
Though the use of these prior art placement devices presents advantages over the previously described placement methods, these devices also possess certain deficiencies which detract from their overall utility. It has been observed that the attachment of the base portions of these prior art placement devices to a concrete form or frame member 14 often requires the use of multiple fasteners, which makes the attachment process a difficult and time-consuming task.
It is an object of the present invention to address the deficiencies of the prior art discussed above and to do so in an efficient, cost effective manner.